The present invention relates to a method of controlling communication resources in a communication system, particularly a mobile telephone system.
In communication systems such as mobile telephone systems, the system possesses a given capacity of information transfer resources that can be used for establishing connections to the system users. The different types of connections requested by users have widely varying requirements in information transmission quality. For instance, while a voice signal is rather tolerant of transmission errors, it is virtually intolerant of transmission delay. On the other hand, program files to be transferred from one computer to another must not contain a single transfer error, whereas their transfer is fairly tolerant of transmission delay.
Broadly speaking, information transfer techniques can be categorized into circuit-switched and packet-switched methods. In circuit-switched networks, certain continuous communication resources which are de-allocated only at the release instant of the user circuit are allocated for the use of the connection during the establishment step of the connection. By contrast, a plurality of different packet-switching communication protocols in the technology of packet-switched networks are known, whereby the connection established between terminal equipment and a base station is not continuous, but the information is carried instead in the form of packets with sequential transmission which have separating intervals of varying duration. Here, one benefit over circuit-switched networks is attained in that the radio resources required for a given connection are not needlessly reserved when a temporary pause occurs in the information transfer.
In packet-switched networks, the packets serving the information transfer of a number of separate connections utilize the same communication resources which can perform the transmission of a single packet at a time. As a result, the packets must queue for their allocated transmission position in the packet transmission sequence, which causes a greater transmission delay in packet-switched networks than in circuit-switched networks. Generally speaking, it can be said that a circuit-switched connection is advantageously used for connections requiring a short transmission delay, such as voice signals, while a packet-switched network is suitable for connections tolerant of longer transmission delays.
For optimal service of connections of different types, the system should have a dual capability of both flexibly forming short-delay circuit-switched connections and simultaneously serving packet-switched connections with maximum utilization of information transfer resources. One conventional system capable of establishing both circuit-switched and packet-switched connections is a GPRS (General Packet Radio System) system adapted to operate in conjunction with a GSM (Global System for Mobile Communications) system. Here, the resources are allocated both permanently and dynamically between the two systems, whereby the resources allocated to the GSM system are used for establishing circuit-switched connections and the GPRS system resources serve packet-switched connections. However, if the GSM system does not occupy the channel defined by the allocated time slot, due for instance to a silent interval in the voice communication, the unused capacity of the channel cannot be utilized by the GPRS system.
Finnish patent application No. FI 964308, which at the filing date of the present application has not yet been disclosed to the public, is for a method of dividing the resources of the radio communication channel between the base station and the terminal equipment into frames which may be further subdivided into smaller units. Each frame has a two-dimensional structure. The first level of frame subdivision is based on time, which means that each frame is given a certain time duration which may be further subdivided into consecutive time slots. In a preferred embodiment of the invention, each frame contains a constant number of time slots, but the allocation of the time slots may vary from one frame to another. The second level of frame subdivision is based on time, frequency, or code. If the second subdivision level is also time-based, each time slot of a frame is further subdivided into smaller slots. If the second level of frame subdivision is frequency-based, the frame as a whole reserves a given frequency band, from which narrower sub-bands, or frequency channels, can be allocated for each time slot of a frame. When the performance of the second level of frame subdivision is code-based, a certain number of mutually orthogonal codes are allocated to each time slot. Obviously, it is possible when so required to subdivide the slots obtained by-division according to two of these subdivision variables into yet smaller allocation units on the basis of the third subdivision variable. The smallest resource unit that can be allocated from a given frame is called a slot, and an individual slot is always allocated for the sole use of a given connection.
FIG. 1 shows a variation of a two-dimensional frame according to prior art. As noted above, the first dimension of the frame is time, while the other dimension may be time, frequency or code. In the case of FIG. 1, the second subdivision of the frame is either time-based or code-based. The size of the frame in both dimensions must be so determined that the frame meets all other specifications of the system. In the illustrated example, the duration of the frame on the time scale is about 4.615 milliseconds, which is time-divided into eight time slots, each time slot reference numeral 15 having a duration of about 0.577 ms. The frequency bandwidth of the frame is about 1.6 MHz. When the second subdivision is time-based, the smallest contiguous units, or slots, of the frame have a bandwidth of 1.6 MHz, whereby their duration on the time scale may be 0.577 ms, or alternatively 0.114 ms. Reference numeral 16 designates a larger slot with dimensions 0.577 msxc3x971.6 MHz, and reference numeral 17 designates a smaller slot with dimensions 0.114 msxc3x971.6 MHz. When the second subdivision is code-based, the slots have a bandwidth of 1.6 MHz with 0.577 ms duration, but varying types of codes are used in the different slots. When code type 1 is used, the time slot can be allocated to only one connection at a time. When code type 2 is used, the same time slot can be utilized by four connections simultaneously. Because the use of a code increases the amount of information to be transferred, the overall quantity of information transferable by code type 2 remains smaller than with code type 1.
Resource allocation using the prior art techniques described above offers efficient facilities for serving the needs of connections of different types. However, there is no known method capable of controlling the allocation of communication resources such as radio resources in a sufficiently flexible and dynamic manner between connections having different requirements.
The object of the present invention is to fulfill this need by means of a method and apparatus described in the appended independent claims.
The purpose of the invention is to form various kinds of communication services for different types of connections, optimally using a common communication resource.
In the method of the invention, connections are divided into at least two different connection classes according to their requirements for transmission delay. The control system of the base station subsystem maintains a record of the transmission needs of the users logged in the different categories and divides the available radio resources into slots of suitable capacity on the basis of this recorded information.
For connections with stringent requirements regarding transmission delay, circuit-switched connections are allocated with a bandwidth which can be controlled dynamically. Then, from the resource pool still unassigned after resource allocation to the circuit-switched connections, a sufficient amount of resources per allocation period are allocated on a time-limited basis to connections having a higher tolerance for delay so as to accomplish transmission, such as the transmission of a given amount of data. The allocation period comprises one or more time frames. Resources in the different transmission directions are allocated independently of each other.
According to one embodiment, the class of connections with a higher tolerance for delay is further divided into at least two subclasses according to the quantity of information to be transferred. For connections requiring only low volumes of information, a traffic channel is allocated for a limited time which is sufficient to transmit a given amount of data. For connections requiring the transference of high volumes of information a reservation identity RID is allocated. The RID is then used to signal the allocation of communications resources of subsequent allocation periods.